These throw-away devices automatically retract the lancet after the tip has momentarily projected, and they are designed so that it is virtually impossible to get at the lancet after such use. However, such an objective is not always achieved, and by using a tool, for example, it is sometimes possible to reset the lancet.
Another problem facing the designer of such a device is to make it as simple as possible, with the minimum number of parts to manufacture and assemble. If the device is to be thrown away after a single use, anything too complex is costly and unacceptable.